The aim of this study is to define the change of plasma high density lipoprotein-cholesterol (HDL-C) in the spontaneously diabetic Chinese hamsters in the Asahikawa colony (CHA). These animals were divided into two groups according to fasting plasma glucose level; non-diabetic group and diabetic group. Plasma HDL-C was measured by a microliters-scale ultracentrifugal method using an RPL-42T rotor (Hitachi Koki Co.). The diabetic hamsters had hypoinsulinemia and hyperlipidemia. Plasma HDL-C in the diabetic group was significantly elevated as compared with the non-diabetic group. A significant positive correlation was observed in both groups between plasma HDL-C and total cholesterol. The male hamsters tended to have higher plasma HDL-C and total cholesterol levels than the female hamsters in either group. Moreover, an electrophoretic analysis showed that there was some relative increase in plasma very low density lipoprotein, low density lipoprotein and high density lipoprotein (HDL) in the diabetic hamsters. An ultracentrifugal analysis showed that plasma chylomicron appeared only in the diabetic hamsters. The heterogeneity of particle size of HDL was found by gradient gel electrophoresis. The apparent average molecular weight of HDL was approximately 265,000 in either group. It is concluded that plasma HDL-C increased with the advance of hyperglycemia and hyperlipidemia in insulin-deficient diabetic hamsters and that there was sex difference in the hamsters for plasma HDL-C and total cholesterol.